This invention relates to ladles for molten metal, and particularly to liners for such ladles.
Ladles for molten metal are generally in the form of a truncated cone made of iron or steel having internal linings of refractory material. Initially the liner materials, namely silica, aluminum and magnesite based materials, were mixed with an inorganic binder to form a refractory layer which could withstand the high pouring temperatures and corrosive slags of ferrous metals. The materials were either hand rammed into place or poured/packed around a form to produce the inside shape of the ladle.
One form of ladle for molten metal, known as a teapot ladle, is distinguished by a spout, extending from the bottom of the ladle to its top edge, or lip, thus ensuring the provision of clean metal to the mold from the interior of the ladle.
Using traditional refractory practices, foundries can produce the spout of the teapot design in many ways. For example a half round or flat refractory tile can be embedded into the internal cylindrical sidewall of the refractory liner. However, all conventional refractory materials used must be preheated, at considerable cost, to avoid chilling the metal and to prevent thermal shock to the refractory.
In the early 1980's KALTEK (RTM) shank ladle liners were introduced. These are one-piece linings made of silica, aluminum and magnesite, and are vacuum formed and bonded with an organic material such as phenolic resin to make the product strong (for transportation purposes) when cured. These liners are low density and low thermal conductivity and are thus insulating by nature, compared to conventional refractory liners. They do not last as long as conventional refractory liners, and thus the material costs are greater. However, being easy to install without the need for special equipment, insulating by nature, frequently changed out and not requiring preheat, there are many advantages, such as lower labour and energy costs, lower employee injury, better metal temperature control, lower scrap rates and no pre-heat costs.
In use, a layer of coarse sand is poured into the bottom of an empty ladle shell and the KALTEK (RTM) liner is placed inside the shell on the bed of sand and levelled With the top of the ladle shell. More sand is poured between the liner and shell until a level slightly below the top of the liner is achieved. A capping material is then applied to the void below the top of the liner to prevent the sand from coming out of the ladle during the pouring when the ladle is tipped forward. The capping material can be any self drying material such as aqueous sodium silicate mixed with sand. The capping material is vented allowing gas from the organic binder to escape when metal is poured into the ladle.
Upon the introduction of KALTEK (RTM) liners, consideration was given to the development for a teapot ladle of a KALTEK (RTM) liner of cylindrical or truncated cone shape having a pouring spout to serve as part of a teapot ladle system.
Initially it was proposed to use a straight/flat tile (dam or barrier plate) embedded into the liner internal sidewall to form the spout. Such a proposal is shown in FIG. 1, with the tile 10 being embedded, with refractory mortar, into grooves in the inner sidewall 11 of the liner 12, so as to define a spout 13, through which poured metal flows, in use. A similar liner for a teapot ladle is shown in FIGS. 2 and 3 of U.S. Pat. No. 4,330,107, where again the flat tile is embedded in the sidewall of a KALTEK (RTM) liner.
With the flat tile itself being of KALTEK (RTM) material, it was found that it did not last as long as required to justify its high cost before it broke.
Moreover, the KALTEK (RTM) material was found to gas into the metal contained in the liner because its organic components burn out on contact with the high metal temperatures. In the walls (i.e. the body) of the ladle lining, the resultant gases exit through the backing sand, causing no problems. Unfortunately the dam or barrier plate is surrounded on both sides with molten metal, causing excess hydrogen and nitrogen pickup in the metal itself. This creates defects in the final castings.
Making the flat tile of conventional refractory/ceramic material was never implemented as, although a longer life could be expected, it would be of very high cost and would be expected to cause a chill effect on the metal mentioned above.
An alternative solution attempted was to use a half-round tile (dam or barrier plate) embedded into the liner internal sidewall to form the spout. Such a proposal is shown in FIG. 2, with the tile 14 being embedded, with refractory mortar, into grooves in the inner sidewall 11 of the liner 12 to define a spout 15, through which metal flows, in use.
With the half-round tile being of conventional refractory/ceramic material, it was found that it cracked due to ‘thermal stress’ related to its curved shape. Additionally it sometimes came loose from the grooves. Its cost was however lower than a flat tile, because its shape allows it to be smaller. It was never contemplated making the half-round tile of KALTEK (RTM) material, as this would have been expensive due to the need for complex tooling. The KALTEK (RTM) material would still gas into the metal excessively and such a tile would not have been expected to have a life any longer than a flat tile, perhaps shorter.
To overcome this problem of producing a KALTEK (RTM) liner for a teapot ladle, a solution was developed in 1987 which involved using a smaller (less wide), flat, cast refractory or ceramic tile (dam or barrier plate) 16, thus decreasing the cost, fitted at the periphery of the circular section liner 17, as shown in FIG. 3. In order not to close off the bottom opening of the spout 18 partly defined by the tile faster than the top, resulting in an inability to achieve cost, flow rate and thermal performance objectives, the circular section liner had to be provided with an externally curved, outward hollow extension 19 extending downwardly the whole length of the liner below the upper lip.
Insulating tiles, e.g. of KALTEK (RTM) material, were not used in this new design, because they did not possess the longevity required, and because the organically bonded KALTEK (RTM) material would gas excessively.
Although this new design works well, with the tile being of lower cost due to its smaller size, it suffers from the disadvantage that most foundry ladles in which the liner would be set had to be modified to include room for the extension 19. Most such ladles are of cylindrical cross-section with various lip designs to fit their specific application or moulding line layout. Modifying and rebalancing the ladle costs time and money and often results in delays of product trials.